It was a trial and a torment to sailors when it was brought home to them that the magnetic needle did not point truly to the north, but ‘northeasted and northwested’ as they described it. ‘El nordeaster de las agujas pone alos mareantes en muches dudas’, wrote one of them, and many flatly refused to believe it, putting discrepancies down to the use of a faulty lodestone or to bad workmanship on the part of the compass-maker. In the far-off days when the use of ‘needle and stone’ to recover lost bearings was first discovered, they believed that by some magic or divine sympathy the needle turned and pointed to their star, which they called the Shipman's Star, or Stella Maris, the only one that never moved. But Peter Peregrinus, writing the first scientific treatise on magnetism in 1269, remarked that they were wrong. The needle pointed to the celestial pole, round which the Pole Star circled like any other. And three centuries later Peter in his turn was faulted by the Elizabethan mathematician John Dee, who scribbled a note in the margin of the medieval writer's book to the effect that it was neither the star nor the pole which was the centre of attraction, but a spot on the Earth—the magnetic pole.